Conventionally, in the manufacturing process of automobiles, the fixing of components to a plurality of locations on a work by screws or bolts has been performed using a fastening device.
For example, this fastening device includes a robot arm and a nut runner provided to a leading end of this robot arm (refer to Patent Document 1). Then, a bolt is retained by a socket of the nut runner, and when a component is conveyed in a state temporarily fixed to the work, the robot arm is controlled to insert the bolt retained in this nut runner into a predetermined location of the work. Thereafter, the socket is made to rotate to fasten the bolt.
However, in recent years, a plurality of types of vehicle models have been manufactured on one line, as a result of which it has been demanded for a plurality of types of bolts to be fastened with one fastening device. Therefore, the following such fastening device has been proposed (refer to Patent Document 2).
Specifically, the fastening device of Patent Document 1 includes a plate-shaped pallet to which a socket is mounted, and a nut runner arranged below this pallet. A bolt is retained in the socket. According to this fastening device, first, the rotational shaft of the nut runner is made to ascend to fit together with the socket, whereby the socket is mounted to a lead end of the rotational shaft. Next, the socket mounted to the leading end of the nut runner is made to ascend slightly by moving the nut runner, after which this socket detaches from the pallet by moving in a horizontal direction. Thereafter, the nut runner is made to ascend again to make the socket approach a predetermined position on the work, and the bolt is fastened. Subsequently, the nut runner is made to descend and the head is mounted to a magazine again.
However, since the bolt is retained to the socket of this nut runner, a bolt loading device is used. Relative to bolts that have been aligned in advance, the bolt loading device makes the socket approach the head of a bolt from above the bolt while rotating, and matches the phase with the head of the bolt, thereby fitting the bolt and the socket (e.g., refer to Patent Document 3).    Patent Document 1: Japanese Patent No. 2929879    Patent Document 2: Japanese Unexamined Patent Application Publication No. H7-60567    Patent Document 3: Japanese Unexamined Utility Model Application Publication No. H3-96137